In combustion exhaust gas from incinerators for city garbage, besides SOx, NOx and the like, a small amount of virulently poisonous dioxins is contained, and variety of technologies has been proposed to remove dioxins.
For instance, in the first patent document, a technology for removing dust, SOx, NOx, dioxins and the like contained in gas exhausted from incinerators is disclosed. In this technology, after feeding the gas from incinerators to the first heat exchanger to recover heat, dust is collected through a cyclone and an electric precipitator; SOx and NOx are removed through a scrubber; the exhaust gas is heated by the secondary heat exchanger up to 100 to 200; further harmful components are adsorbed by activated carbon powder added; and a bag filter collects the activated carbon powder filtered.
Further, the second patent document discloses an exhaust gas processing device using adsorber such as activated carbon for removing harmful substances such as dust, dioxins and halogenation organic compound including PCBs. The device comprises: an electric precipitator for removing dust such as ash mixed in exhaust gas from an exhaust gas source to effectively use the adsorber even when the concentration of the dust in the exhaust gas is high; an adsorber adding device for adding adsorber such as activated carbon to the exhaust gas of which dust are removed through the electric precipitator; and a bag filter, through which the exhaust gas with the adsorber passes, to filter the adsorber in the exhaust gas.
Besides the above methods of adsorption with activated carbon or the like, the third and fourth patent documents disclose exhaust gas processing devices that soak water with ozone, and spray the ozone-contained water in granular state, through nozzles disposed in a cooling tube, to the exhaust gas flowing in the cooling tube.
Further, the fifth patent document proposes an exhaust gas processing method to remove NOx and dioxins in exhaust gas generated by incinerators for city garbage or the like. The method comprises the steps of: cooling the exhaust gas; introducing the cooled exhaust gas to a bag filter to collect dust including dioxins in solid state; heating the gas again; and contacting the exhaust gas together with a reducing agent for denitration including ammonia to a honeycomb-shaped catalyst to simultaneously decompose and remove nitrogen oxide and toxic chlorine compound such as dioxins.
Meanwhile, as illustrated in FIG. 3, a cement burning facility 21 comprises a preheater 22, a calciner 23, a cement kiln 24, a clinker cooler 25 and so on, and cement raw material R, which is fed to the preheater 22 from raw material supplying system, is preheated in the preheater 22, calcined in the calciner 23, burned in the cement kiln 24, and produced clinker is cooled in the clinker cooler 25. Here, the combustion exhaust gas from the cement kiln 24 was processed through desulferization in the preheater 22 and dust collection using an electric precipitator 26 since limestone as a main raw material has a property to adsorb SOx, and processed combustion exhaust gas was discharged in the atmosphere through a fan 27 and a stack 28.
Patent document 1: Japanese Patent Publication 2001-272023 gazette
Patent document 2: Japanese Patent Publication 2003-117343 gazette
Patent document 3: Japanese Patent Publication 2000-185217 gazette
Patent document 4: Japanese Patent Publication 2003-24746 gazette
Patent document 5: Japanese Patent Publication Heisei 7-75720 gazette